High performance sports cars or racing cars present special control and handling problems to designers and drivers. Often, these types of cars travel at such high speeds, and are so aerodynamic in design, that the body of the car generates an upward lift force. The lift force generated may be so strong as to affect the handling of the car. Aerodynamic drag and moments are also generated and can affect handling and safety.
In an effort to remedy such dangerous handling problems, and to improve cornering performance, it is common to see very large horizontal "wings" on high performance sports cars or racing cars. An example of these horizontal surfaces on racing cars is depicted in FIGS. 1a and 1b. These horizontal wings are often three-dimensional airfoils, which have an inverted camber such that as air passes over them, a down force (or "negative lift") is imparted on the vehicle. This down force can overcome the undesired lift force generated by the vehicle's body and improve the vehicle's handling characteristics.
Obviously, it is a goal of high performance racing car designers to achieve a strong down force on the car. As noted above, attempts to remedy handling problems include using horizontal surfaces, such as inverted airfoils/wings, attached to the upper body of the ground vehicle (both fore and aft). Inverted airfoils generally can provide down load (negative lift) and pitching moment to control the vehicle. The need for down load is so critical with specialized racing vehicles, such as Formula One and Indianapolis-type cars, that it is common to see inverted airfoils on both the front and rear sections of these vehicles. In addition, multiple rear horizontal wings are commonly used to generate additional down force on the vehicle.
At one time, it was common to shape the bottom body panels of the vehicle in order to create additional negative down load. This was used to either augment the effect of the inverted wings or to replace the wings. However, current racing rules prohibit this type of design in many racing categories. Therefore, many racing cars are restricted to using size-limited inverted airfoils on the front and rear of the car and no curvature of the lower body in order to generate the necessary down load and pitching moment. Although these inverted airfoils do generate negative lift, which increases with the square of the vehicle's speed, such airfoils have a number of inherent drawbacks.
Initially, inverted airfoils/horizontal wings are mechanically complex and heavy. These wings also require supporting structures, which increase the drag force on the vehicle and increase the weight penalty paid for the horizontal surface itself. For example, inverted airfoils on the aft of the car are often supported by two vertical plates. See FIGS. 1a and 1b. These plates add weight, disrupt the flow of air over the car, and increase the drag upon the vehicle.
In an effort to increase the down force, the wings used often have highly cambered airfoil sections or use flaps to increase the effective camber of the airfoil. Highly-cambered airfoils, especially those with flaps, create much higher profile drag for the vehicle. Thus, the aerodynamic efficiency of these wings decreases. Additionally, if flaps are used to increase the camber, the mechanical complexity and weight of the vehicle increases. Greater mechanical complexity obviously creates a greater chance for mechanical failure.
The prior art solutions to high-performance vehicle handling problems exhibit other inherent problems. Technical regulations on racing cars and cost practicality on high performance sports cars frequently prohibit the use of mechanical adjustments to modify the airfoil during travel/racing. Therefore, these wings are "point designs." That is, they are optimum only at one particular driving condition, even though a given race or journey may require different optimum down forces for high-speed straightways and for lower-speed turns. While wings designed to generate a smaller down force at higher speeds may not remedy the handling problems described above in slower speed turns, wings designed for large down force at slower speed turns may generate far too much down force at high speed. Too much down force compresses the suspension, bottoms the car on the road and seriously degrades the vehicle's handling. Even if it were within the regulations, or realm of cost practicality, to adjust the angle of attack of the horizontal wings, the weight penalty for such a mechanical component could be substantial. As such, the prior art solution for down force requirements is only efficient at one operating condition of the many faced by high performance ground vehicles.
Under normal driving conditions, a car pitches due to road irregularities, braking, and acceleration. All these occurrences cause changes in angle of attack of the fore and aft wings, which can produce unbalanced lift distributions and cause the car to experience dynamic pitch instabilities. Fixed horizontal wings cannot respond to these problems adequately.
Additionally, the wings employed are not the best lift-producing devices available. The wings used are usually low span and thus lower aspect ratio. Low aspect ratio necessarily causes higher induced drag and strong vortex flow fields. The typical design for these wings on ground vehicles usually does not exceed a lift coefficient of around 4.0. Of course, the particular lift force generated during travel can vary substantially and is proportional to the vehicle speed squared.
Thus, there exists a need for a light-weight, simple, non-moving, dynamically adjustable system for producing variable down forces of much higher magnitudes, with or without drag generation, on a high performance ground vehicle, or racing car. Such system would overcome the many problems of the prior art. It is to the provision of such methods and apparatuses that the present invention is primarily directed.